Bradford sixth-form students could have exam deadlines extended and receive extra marks because of the chaos caused by the winter vomiting bug.

More than half the secondary schools in the district are now banning visitors in an attempt to stop the sickness spreading.

Ten Bradford schools were due to be shut today, including three secondaries, and 71 schools have restrictions in place preventing visitors.

There have been 42 school closures or partial closures in Bradford because of the winter vomiting bug since February.

Bradford schools run joint A-levels and post-16 courses as part of the Bradford Confederations, which see secondary schools sharing resources.

But restrictions on teachers and pupils visiting other schools mean they have missed lessons. And now schools are contacting examining boards for help.

Hanson School in Swain House operates joint post-16 courses with Immanuel CE Community College in Idle, with students bussed between the two sites. But pupils cannot attend each other's school because Hanson is under restriction.

Hanson's assistant head teacher, Derek Needham, said pupils were being e-mailed work and study workshops were planned to catch up once the restrictions are lifted. But the school has contacted examining boards to inform them.

Mr Needham said: "The exam boards have told us that they can extend coursework deadlines and offer an additional five per cent in marks."

This was a standard response and not a special exception made for Bradford.

St Bede's Grammar School and St Joseph's Catholic College also stopped joint sixth form lessons yesterday as both have been affected by the winter bug.

Challenge College's head teacher, Sian Harris, said she had been told the school's sixth form students could receive an extra one per cent because of the disruption .

The school in Frizinghall has been under restriction for two weeks and had cancelled its joint sixth form lessons with Laisterdyke Business and Enterprise College. But the school has now decided to reinstate the lessons as both schools have been affected by the winter bug.

Sian Harris said: "It seems ridiculous that pupils are missing half their lessons seven weeks before their A and AS levels so we have decided to restart it."

Carlton Bolling College in Undercliffe, Nab Wood School and St Bede's Grammar school in Heaton were all due to be shut today because of pupil sickness.

The bug is also affecting primary schools with parents prevented from attending activities, after-school and breakfast clubs. Parental involvement workers are employed across 49 primary schools around the district.

But 20 schools have had to cancel such work as mums and dads are not allowed into the school buildings.